Fixed invalid usage of ATOMIC_FLAG_INIT in libprocess.
Fixed invalid usage of ATOMIC_FLAG_INIT in libprocess.

Review: https://reviews.apache.org/r/43859/

verizonlabs/mesos,dforsyth/mesos,reneploetz/mesos,chhsia0/mesos,kaysoky/mesos,dforsyth/mesos,neilconway/mesos,verizonlabs/mesos,neilconway/mesos,reneploetz/mesos,reneploetz/mesos,kaysoky/mesos,andschwa/mesos,Gilbert88/mesos,Gilbert88/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,verizonlabs/mesos,neilconway/mesos,chhsia0/mesos,neilconway/mesos,gsantovena/mesos,kaysoky/mesos,zmalik/mesos,andschwa/mesos,asamerh4/mesos,dforsyth/mesos,andschwa/mesos,gsantovena/mesos,yuquanshan/customizedMesos,dforsyth/mesos,asamerh4/mesos,gsantovena/mesos,yuquanshan/customizedMesos,gsantovena/mesos,Gilbert88/mesos,reneploetz/mesos,dforsyth/mesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,Aman-Jain-14/customizedMesos,asamerh4/mesos,reneploetz/mesos,abudnik/mesos,Aman-Jain-14/customizedMesos,jpeach/mesos,yuquanshan/customizedMesos,chhsia0/mesos,andschwa/mesos,jpeach/mesos,neilconway/mesos,kaysoky/mesos,chhsia0/mesos,craimbert/mesos,craimbert/mesos,abudnik/mesos,verizonlabs/mesos,kaysoky/mesos,gsantovena/mesos,asamerh4/mesos,craimbert/mesos,zmalik/mesos,kaysoky/mesos,Gilbert88/mesos,abudnik/mesos,jpeach/mesos,gsantovena/mesos,jpeach/mesos,yuquanshan/customizedMesos,yuquanshan/customizedMesos,zmalik/mesos,verizonlabs/mesos,reneploetz/mesos,abudnik/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,abudnik/mesos,chhsia0/mesos,zmalik/mesos,zmalik/mesos,andschwa/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,dforsyth/mesos,verizonlabs/mesos,asamerh4/mesos,jpeach/mesos,andschwa/mesos,craimbert/mesos,yuquanshan/customizedMesos,abudnik/mesos,chhsia0/mesos,gsantovena/mesos,asamerh4/mesos,abudnik/mesos,dforsyth/mesos,zmalik/mesos,reneploetz/mesos,Gilbert88/mesos,Aman-Jain-14/customizedMesos,neilconway/mesos,asamerh4/mesos,zmalik/mesos,jpeach/mesos,craimbert/mesos,chhsia0/mesos,craimbert/mesos,jpeach/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,andschwa/mesos